Continuous, four vessel processes for the production of poly(ethylene terephthalate) are known. For example, Sheller, U.S. Pat. No. 3,438,942 discloses a process for the continuous production of poly(ethylene terephthalate) comprising ester exchange followed by three polycondensation steps.
Also known are batch processes for the production of poly(trimethylene terephthalate). For example, Doerr et al., U.S. Pat. No. 5,340,909 discloses the production of poly(trimethylene terephthalate) using either an ester exchange reaction starting with lower dialkyl terephthalate ester or direct esterification of terephthalic acid followed by a polycondensation reaction, both of which are carried out in batches using an autoclave.
It would be highly desirable to provide a continuous, four-vessel process for the production of poly(trimethylene terephthalate). It would also be desirable to provide a continuous process for the production of poly(trimethylene terephthalate) in which the production of by-products, such as acrolein and allyl alcohol, is minimized, and in which the molecular weight of the final poly(trimethylene terephthalate) polymer is maximized. The present invention provides such a process.